The objective of this study is to evaluate intracortical inhibition (ICI) in focal dystonia and in generalized dystonia of known genetic origin (DYT1 dystonia) in order to determine whether abnormalities of ICI can represent a marker of genetic predisposition for the development of dystonia. It is unclear why some carriers of the DYT1 dystonia do not develop dystonic symptoms. One possible explanation is that the development of dystonia is a two-stage process: first, loss of ICI (which may be genetically determined) and, second, exposure to an environmental trigger such as excessive repetitive movements. Thus we hypothesize that impaired ICI may serve as a marker for the DYT1 carrier state. There is good evidence that focal dystonia is a genetically determined disorder, but the gene responsible remains undetermined. We hypothesize that, in up to 50% of first degree relatives of patients with focal dystonia, impaired ICI may be found which would serve as a gene marker for the abnormality. In those individuals with this genetic marker of impaired ICI, further linkage analysis studies could be performed to identify the causative gene. In this study, we propose to measure ICI using transcranial magnetic stimulation in patients with both focal and generalized forms of dystonia, their first degree relatives and an age matched control group.